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Porous and heteroatom-doped carbon nanostructures were investigated to address the low specific capacity and poor rate capability of the graphite anode. For successful application to commercial lithium-ion batteries, the electrochemical performances of the porous and heteroatom-doped carbon nanostructures should be evaluated in the full-cell operating voltage window. Herein, polyvinylpyrrolidone (PVP)-derived carbon nanospheres with various morphological and atomic structures were prepared by electrospraying and controlled thermal-treatment processes conducted under various thermal oxidation termination temperatures. The carbonaceous microstructures, chemical compositions, and pore structures of the PVP-derived carbon nanospheres were thoroughly examined, while their cycling and rate performances were investigated in the voltage range of 0.01–1.5 V (the normal anode operating range of the full-cell). We identified the ideal carbonaceous anode material conditions, i.e., high carbon and nitrogen content with low oxygen content for high and reversible capacity and rate performances, and small particle size with low surface area and porosity for long life. Our work demonstrates that optimizing porosity and heteroatom composition is crucial for developing commercially viable carbonaceous anode materials.

Previous research established that Si–Sn–C ternary composite electrodes composed of carbon nanofibers (CNFs) having robust double-hole structures filled with Si and SnOx nanoparticles displayed excellent electrochemical performance due to the thermodynamic contribution of Sn. This study reports simple and highly commercial ternary composite electrodes. By electrospinning and subsequent thermal treatment, Si and Sn nanoparticles were dispersed in solid CNFs to form Si–Sn–SC nanofibers, or they were incorporated into a core of hollow CNFs to form Si–Sn−HC nanofibers. The rate performances of these two ternary electrodes displayed quite good retention because of the ternary composition, but their rate performances differed at high current densities (5000 and 10,000 mA g–1); the core/shell structure of the Si–Sn−HC nanofibers was more beneficial for rate performance retention than the Si–Sn–SC nanofibers having intimate electrical contact of Sn and Si with the carbon matrix. Improved cycling performances also resulted from the structure of the Si–Sn−HC nanofibers. The core/shell structured Si–Sn–C ternary composite anode thus has an advantageous structure for high-power Li-ion batteries having long-term stability.

Intrinsic self-healing hydrogel materials have been studied by many researchers owing to their excellent durability and high applicability in the biomedical field. Herein, we report a self-healing hydrogel containing dynamic boronate ester bonds. First, low-molecular-weight hyperbranched polyglycerol (LMPG), containing cis-1,2- or 1,3-diols, was synthesized by cationic ring-opening polymerization of glycidol initiated from citric acid. Second, 4-vinylphenyl boronic acid and acrylamide were co-polymerized in the LMPG-containing alkaline solution used for preparing the hydrogel. The composition of vinyl monomers, LMPG, and chemical cross-linker affects the gel-formation and self-healing properties of the hydrogel. Interestingly, the prepared hydrogel with specific composition exhibits excellent extensibility, resulting in 416-fold (41,600%) elongation. The formation of a reversible boronate ester bond by a diol of LMPG and boronic acid of vinyl polymer enables flexible fiber spinning process by reducing the drawing stress. After fiber fabrication is completed, the reversible bonds act as permanent multi-cross-point under absence of water, thereby giving a high tensile strength (128 MPa) to the hydrogel-based fiber.

It is urgent to develop a new anode material that addresses the needs on high energy density as well as high power density of Li-ion batteries to meet the growing demands of high-performance mobile devices and electric vehicles. In this work, a new ternary composite (Si–Sn–C) anode material was designed to achieve exceptional rate performance by scavenging lost Si charge capacity at higher working potential of Sn (~ 0.9 V) under increased current densities. Si and Sn nanoparticles were separately compartmentalized in double-holed carbon nanofibers (Si–Sn–DHCNFs) to elucidate the working potential effect without a kinetic improvement by Sn. Si–Sn–DHCNFs showed high specific capacity (1000 mA h g−1 at 100 mA g−1) and exceptional rate performance (720 mA h g−1 at 10,000 mA g−1). Our work demonstrates that the design of new anode materials is a fruitful route to enhancing the power density of batteries.

In article number 2003155, Jeyoung Park, Dongyeop X. Oh, Sung Yeon Hwang, and co‐workers report a biodegradable, moisture‐resistant, highly efficient, and breathable face mask filter based on easy‐to obtain poly(butylene succinate) coated with chitosan nanowhiskers. Integrated microfiber/nanofiber mats present a particulate matter removal efficiency as high as the commercial N95 filter due to a combination of physical sieving and electrostatic adsorption. [Image: see text]

The demand for face masks is increasing exponentially due to the coronavirus pandemic and issues associated with airborne particulate matter (PM). However, both conventional electrostatic‐ and nanosieve‐based mask filters are single‐use and are not degradable or recyclable, which creates serious waste problems. In addition, the former loses function under humid conditions, while the latter operates with a significant air‐pressure drop and suffers from relatively fast pore blockage. Herein, a biodegradable, moisture‐resistant, highly breathable, and high‐performance fibrous mask filter is developed. Briefly, two biodegradable microfiber and nanofiber mats are integrated into a Janus membrane filter and then coated by cationically charged chitosan nanowhiskers. This filter is as efficient as the commercial N95 filter and removes 98.3% of 2.5 µm PM. The nanofiber physically sieves fine PM and the microfiber provides a low pressure differential of 59 Pa, which is comfortable for human breathing. In contrast to the dramatic performance decline of the commercial N95 filter when exposed to moisture, this filter exhibits negligible performance loss and is therefore multi‐usable because the permanent dipoles of the chitosan adsorb ultrafine PM (e.g., nitrogen and sulfur oxides). Importantly, this filter completely decomposes within 4 weeks in composting soil., An eco‐friendly face mask filter with high‐level functionality is developed. Made only of biodegradable materials, it completely decomposes in the soil, thereby providing a fundamental waste problem solution. Moreover, the filter is a practical alternative to conventional disposable filters by integrating the physical sieving role of a poly(butylene succinate) fiber mat and the permanent electrostatic adsorption roles of chitosan nanowhiskers.

To address environmental concerns related to the large volume of plastics currently used, high-performance, sustainable, and satisfactorily performing bioplastics can be a solution. Isosorbide (ISB)-based amorphous poly(arylene ether sulfone)s (PAESs) derived from biomass feedstocks instead of harmful aromatic petrochemicals, such as bisphenol-A (BPA), are promising novel materials. To expand the range of eco-friendly products, ISB-PAES microfibers (ISU) along with BPA-PAES-based microfibers (PSU) have been fabricated through dry-jet wet spinning. ISU is mechanically 2.3 times stronger (247 MPa) than PSU (106 MPa), which may be ascribed to the compact and homogeneous structure of ISU compared to the porous structure of PSU. This structural superiority is due to the polar ISB moiety, which improves the phase stability of the ISU spinning dope in water (a role of the coagulant). For potential wig applications, the diameter, strength, and moduli of ISU are well matched to those of human hair. In addition, ISU is easily colored and endures high temperatures better than current wig filaments. It survives at high temperatures without breaking down during hair iron treatment (200 °C).

Electrically tunable colloidal photonic crystals (ETPCs) have been investigated because of several merits such as easy color tunability, no discoloration, and clear color. The coloration mechanism of ETPCs has been explained in terms of only the electric field. Herein, we report on a new mechanism: electric field plus redox reaction. Specifically, the coloration behavior of ETPCs was investigated under electrically conductive or insulated conditions using current-voltage, cyclic voltammetry, and zeta potential measurements, as well as scanning electron microscopy. Electrophoretic movement of ETPC particles toward the positive electrode was caused by the electric field due to the particles' negative surface charge. At the positive electrode, ETPC particles lost their electrons and formed a colloidal crystal structure. Finally, an ETPC transparent tube device was constructed to demonstrate the coloration mechanism.

TiO2@SnO2@TiO2 triple-shell nanotubes are fabricated using electrospun polyacrylonitrile (PAN) nanofiber template and plasma-enhanced atomic layer deposition (PEALD). The triple-shell nanotubes have a uniform diameter of ~200 nm, and the thickness of each shell is ~10 nm. The triple-shell nanotube electrode exhibits high reversible capacity of 550 mA g−1 after 60 cycles at the current density of 50 mA g−1, stable cyclability, and high-rate performance (296 mA g−1 at high current density of 5 A g−1) as an anode for lithium-ion batteries. The excellent electrochemical properties are attributed to the structural robustness of the triple-shell nanotubes against pulverization.

This work reports a novel design strategy for a strong polyacrylonitrile (PAN) fiber using an electrochemical wet-spinning process. First, a spinning dope was prepared using PAN copolymer containing methyl acrylate. This was spun using a conventional wet-spinning setup, but with a special nozzle spinneret whereby an electric potential could be applied. In situ electrochemical oxidation of methyl acrylate was then induced within the nozzle, resulting in electrochemical demethylation of the PAN copolymer. The subsequently endowed hydrophilic and hygroscopic properties of the PAN fibers improved the chain mobility of the PAN molecules and reduced void formation during wet-spinning. Investigation of the quantitative relationships between the degree of electrochemical demethylation and the mechanical properties of the PAN fibers clarified the in situ plasticization effect of absorbed water induced by the electrochemical demethylation. The Young's modulus and tensile strength of the PAN fibers were improved by 23.4% and 23.5%, respectively, and the breaking strain was increased by 28.1%. These results demonstrate the innovativeness of our new electrochemical wet-spinning process.

A facile method is developed to improve the initial reversible capacity of hollow carbon nanofibers (HCNFs), which are manufactured via coaxial electrospinning of core/shell precursor nanofibers and their thermal treatments for stabilization and carbonization. Since the low initial reversible capacity of HCNFs is mainly caused by mesopores in the HCNFs, in our approach, the size of these mesopores is reduced by simply introducing a chemical vapor deposition (CVD) process between the stabilization and carbonization processes, thereby inducing the deposition of carbon atoms in the mesopores. The initial coulombic efficiencies of the HCNFs and the Si-encapsulated HCNFs are significantly increased by employing CVD process. The mechanism behind such improvement is revealed by morphological, microstructural, surface, and electrochemical analyses, confirming that control of the mesopores in HCNFs is an effective means to improve the electrochemical performance of HCNFs.

This paper reports on a fabrication method to manufacture cylindrically multi-channeled hollow carbon nanofibers (mcHCNFs). Polyacrylonitrile nanofibers with cylindrical multi-cores of poly(styrene-co-acrylontitrile) (SAN) were first electrospun using a specific nozzle and subsequently heat-treated, leaving vacant or silicon (Si)-encapsulated mcHCNFs. The latter was obtained by dispersing Si nanoparticles in the SAN solution. Investigations into the morphologies, microstructures, and material compositions of the resulting mcHCNFs demonstrated that Si-encapsulated multi-channels were formed in a controlled, uniform manner. The multi-channel effects were evaluated by characterizing the anodic properties of Si-encapsulated mcHCNFs using galvanostatic charge–discharge tests. More contact between the Si nanoparticles and the carbon shell in the Si-encapsulated mcHCNFs brought about improved discharge capacity and capacity retention.

Electrospinning, a common method for synthesizing 1D nanostructures, has contributed to developments in the electrical, electrochemical, biomedical, and environmental fields. Recently, a coaxial electrospinning process has been used to fabricate new nanostructures with advanced performance, but intricate and delicate process conditions hinder reproducibility and mass production. Herein, recent progress in new emerging parameters for successful coaxial electrospinning, and the various nanostructures and critical application areas resulting from these activities. Relationships between the new parameters and final product characteristics are described, new possibilities for nanostructures achievable via coaxial electrospinning are identified, and new research directions with a view to future applications are suggested.

Adsorption and growth behaviors of fibroblast cells have been studied on poly(styrene- ran -acrylic acid) (PS- y -AA) films with four different degrees of charge contents ( y = 0%, 5.6%, 10.0%, and 15.3%) and tissue culture polystyrene (TCPS). The structures and adsorption behavior of fibroblast cells were found to be quite different as a function of charge density. As the degree of charge density of PS- y -AA is increased, more cell adhesion and proliferation were observed. However, there was no significant difference in the adsorption of fibroblast cells in the absence of serum, indicating that serum proteins may play a critical role in the adhesion of cells to carboxylic acid groups.

A new nozzle system for the efficient production of multi-layered nanofibers through electrospinning is reported. Developed a decade ago, the commonly used coaxial nozzle system consisting of two concentric cylindrical needles has remained unchanged, despite recent advances in multi-layered, multi-functional nanofibers. Here, we demonstrate a core-cut nozzle system, in which the exit pipe of the core nozzle is removed such that the core fluid can form an envelope inside the shell solution. This configuration effectively improves the coaxial electrospinning behavior of two fluids and significantly reduces the jet instability, which was proved by finite element simulation. The proposed electrospinning nozzle system was then used to fabricate bi- and tri-layered carbon nanofibers.

Silicon/carbon (Si/C) nanocomposites have recently received much attention as Li-ion battery negative electrodes due to their mutual synergetic effects in capacity and mechanical integrity. The contribution of Si to the total capacity of the Si/C nanocomposites determines their structural efficiency. Herein, we report on a multi-layered, one-dimensional nanostructure that exhibits the theoretical specific capacity of Si in the nanocomposite. Concentrically tri-layered, compartmentalized, C-core/Si-medium/C-shell nanofibers were fabricated by triple coaxial electrospinning. The pulverization of Si was accommodated inside the C-shell, whereas the conductive pathway of the Li-ions and electrons was provided by the C-core, which was proven by ex situ Raman spectroscopy. The compartmentalized Si in between the C-core and C-shell led to excellent specific capacity at a high current rate (820 mA h g(-1) at 12000 mA g(-1)) and the realization of the theoretical specific capacity of the Li15Si4 phase of Si nanoparticles (3627 mA h g(-1)). The electrochemical characterization and inductively coupled plasma-atomic emission spectrometry provided direct evidence of full participation of Si in the electrochemical reactions.

We report the effects of various substrates and substrate thicknesses on electrospun poly(vinylidene fluoride) (PVDF)-nanofiber-based energy harvesters. The electrospun PVDF nanofibers showed an average diameter of 84.6 ± 23.5 nm. A high relative β-phase fraction (85.2%) was achieved by applying high voltage during electrospinning. The prepared PVDF nanofibers thus generated considerable piezoelectric potential in accordance with the sound-driven mechanical vibrations of the substrates. Slide glass, poly(ethylene terephthalate), poly(ethylene naphthalate), and paper substrates were used to investigate the effects of the intrinsic and extrinsic substrate properties on the piezoelectricity of the energy harvesters. The thinnest paper substrate (66 μm) with a moderate Young's modulus showed the highest voltage output (0.4885 V). We used high-performance 76, 66, and 33 μm thick papers to determine the effect of paper thickness on the output voltage. The thinnest paper substrate resulted in the highest voltage output (0.7781 V), and the numerical analyses of the sound-driven mechanical deformation strongly support the hypothesis that substrate thickness has a considerable effect on piezoelectric performance.

This work reports the fabrication of double-tubular (or tube-in-tube) carbon nanofibers (CNFs). Tetra-layered nanofibers were manufactured using coaxial electrospinning with a concentric quadruple cylindrical nozzle system. Subsequent heat treatment eroded the first and third layers and converted the second and fourth layers into the carbonized structure, resulting in double-tubular CNFs. The morphologies and microstructures of the two tubes in the CNFs were investigated, revealing that the outer layer possessed denser and higher quality carbon crystals due to the coaxial electrospinning mechanism. Nanoparticles were readily incorporated between the two tubes in the double-tubular CNFs, providing a method for developing new multi-functional one dimensional materials.